Primary glaucoma in the beagle continues to reveal excellent potential as a biochemical model for open angle glaucoma. The disease is being documented by monthly detailed opthalmic examinations and by consecutive photographs of external eyes, iridocorneal angles, and ocular fundi. Studies of inhertance include affected and affected; affected and normal; and "carrier" and affected. The water provocative test will be evaluated by Mackay-Marg tonometry after administration of 50 ml/Kg of water at 37C per os in conscious dogs. The corticosteroid provocative will be investigated in control and glaucomatous beagles by Mackay-Marg tonometry and 0.1 percent dexamethosome qid for 1 month. The mydriatic test will be evaluated in normal and glaucomatous beagles by Mackay-Marg tonometry for 12 hours after instillation of 1.0 percent tropicamide. Schiotz tonography will continue in control and glaucomatous beagles and be compared to constant pressure perfusion in selected glaucomatous dogs. Pilocarpine (l, 4, and 6 percent) will be evaluated by tonometry and tonography in control and glaucomatous beagles. Selected diuretics, i.e., acetazolamide and dichlorphenamide, will also be studied in control and glaucomatous beagles. Fluorescein angiography will be used in glaucomatous beagles to record the vascular changes. Vascular channels in the iridocorneal angle, as depicted by neoprene latex, will be compared in normal and glaucomatous beagles. Aqueous outflow channels will be compared using nitroblue tetrazolium chloride in normal and glaucomatous beagles. Early and advanced glaucomatous globes will continue to be studied by light and electron microscopy.